Process for controlling the porosity of carbon blacks

ABSTRACT

The present invention relates to a furnace black having a STSA surface area of at 130 m 2 /g to 350 m 2 /g wherein
         the ratio of BET surface area to STSA surface area is less than 1.1 if the STSA surface area is in the range of 130 m 2 /g to 150 m 2 /g,   the ratio of BET surface area to STSA surface area is less than 1.2 if the STSA surface area is greater than 150 m 2 /g to 180 m 2 /g,   the ratio of BET surface area to STSA surface area is less than 1.3 if the STSA surface area is greater than 180 m 2 /g, and
 
the STSA surface area and the BET surface area are measured according to ASTM D 6556 and to a furnace process wherein the stoichiometric ratio of combustible material to O 2  when forming a combustion gas stream is adjusted to obtain a k factor of less than 1.2 and the inert gas concentration in the reactor is increased while limiting the CO 2  amount fed to the reactor. Also provided is an apparatus for conducting the process according to the present invention.

The present invention relates to a process for controlling the porosityof carbon blacks, to carbon blacks produced thereby and to an apparatusfor performing the process of the present invention.

BACKGROUND OF THE INVENTION

According to the general knowledge of a person skilled in the art ofcarbon black, as exemplified by “Carbon Black” edited by Jean-BaptisteDonnet et al., second edition, Marcel Dekker, Inc., New York (1993),pages 35 to 39, in a furnace process for making carbon black theporosity of carbon black can be controlled by the quenching position ofthe furnace reactor. The earlier the freshly formed carbon black isquenched, the lower its porosity. The ratio of BET surface area to STSAsurface area may be used as a measure for porosity. In case of blackswith fine particle size this ratio is equal to or slightly less thanunity for very short quenched carbon blacks (no porosity) and greaterthan unity for those produced within longer quench distance. Very fineparticle blacks always exhibit a certain amount of porosity since thequench can only be placed at fixed locations along the reactor. Theoptimum position may not always be available. As a consequence, thereaction may not be terminated at the precise moment at which the carbonblack formation has just been completed. Furthermore, differentresidence times do not only affect porosity, but also the surfacechemistry of the black. The surfaces of very short-quenched blacks arerich in hydrogen from CH groups or those groups which are similar toolefinic double bonds. These surface chemistries may not be desirablefor all applications where carbon blacks commonly can be used.

In tire applications carbon blacks having high surface area and lowporosity can improve the wear resistance of tires. On the other hand iffurnace blacks are produced as described above with a short quenchdistance to achieve high surface area and low porosity the resultantsurface chemistry particularly the olefinic surface groups lead to veryshort vulcanization times which impair the processability of the rubbercompound.

Thus, there is still a need for a process for the production of carbonblacks wherein the porosity of the carbon black can be controlled,particularly reduced, in a furnace process independent of the quenchposition to avoid the above disadvantage of short quenched carbonblacks. There is also particularly a need for carbon blacks that show animproved balance of wear resistance and processability of the rubbercompound in tire application.

According to the present invention the porosity of carbon blacks can beeasily controlled, particularly reduced, in a furnace process byadjusting the stoichiometric ratio of combustible material to O₂ whenforming a combustion gas stream to obtain a k factor of less than 1.2 incombination with increasing the inert gas concentration in the reactorwhile limiting the CO₂ amount fed to the reactor.

In the prior art, carbon black production processes using approximatelystoichiometric combustion were proposed.

U.S. Pat. No. 3,475,125 describes a carbon black production processwherein in the reaction zone at least one stream of hot combustion gasis obtained by burning in a combustion zone a first combustible mixtureof a hydrocarbon fuel and an oxidant, which contains substantially thestoichiometric amount of oxidant required for the burning of said fuel.That first combustible mixture is burned in presence of steam that ispresent in an amount sufficient to protect the refractory lining of saidcombustion zone from excessive temperature. Optionally, at least oneother stream of hot combustion gases which is obtained by burning asecond combustible mixture of hydrocarbon fuel and an oxidant containingan amount of oxidant, which is greater than the stoichiometric amountrequired for the burning of said fuel is applied to the reaction zone.It is described that this process leads to an increased yield of carbonblack while protecting the refractories of the furnace from excessivetemperatures.

U.S. Pat. No. 4,294,814 discloses a process for the production of carbonblack with high structure by axially introducing a first stream ofhydrocarbon feed, by circumferentially or tangentially introducing asecond stream of hot combustion gases into the reactor so as to form avortex of hot combustion gases around the first stream of hydrocarbonfeed and by introducing a third stream of gas radially into the reactor.According to a preferred embodiment, one of the second and the thirdstream comprising combustion gases results from an under-stoichiometricratio of combustible materials and oxygen whereas the other combustiongas stream results from an over-stoichiometric ratio of combustiblematerial to oxygen so that when both combustion gas streams are combinedoverall stoichiometric conditions are achieved with very hightemperatures in the center of the reactor wherein the first stream ofhydrocarbon feed is fed to without contact to the reactor walls.According to the teaching of this prior art document, thereby a carbonblack with very high structure can be obtained.

EP-A 982 378 relates to a furnace process for producing carbon blackwherein a high-temperature combustion gas stream is formed and theoxygen concentration of the combustion gas at the point where thefeedstock is introduced is at most 3 vol.-%. It is described that theadvantage of making the oxygen concentration as small as possible isthat the aggregate size of the carbon black is small and aggregateshaving a large particle size are suppressed. Furthermore, carbon blackshaving a narrow particle size distribution are obtained by that process.

US 2002/0090325 addresses the problem of producing carbon black ofsmaller particle size and narrower aggregate size distribution byconducting perfect combustion of fuel at as high a temperature aspossible and an air ratio close to 1 while restraining damage to thereactor wall refractory in the combustion section. Furthermore, in theprior art section of this reference a Japanese patent application No.10-38215 is discussed that is not related to carbon black production. Inthis Japanese reference a burner combustion method is disclosed whereinthe oxygen concentration is far lower than ordinary air at leastimmediately before the combustion reaction by using dilute air, e.g. byrecycling exhaust gas or diluting the air with inert gas such asnitrogen. In US 2002/0090325 this concept has been considered asunsuitable for carbon black production since if applying such a methodto a carbon black-producing furnace production of carbon black withstabilized quality may become difficult. In addition, diluting oxygenconcentration requires extra cost for equipment. Thus, US 2002/0090325proposes a furnace structure in which an air feed port or ports and afuel feed port or ports are disposed independently, spaced apart fromeach other in the first reaction zone so that combustion air and fuelwill be injected individually into the furnace and burned in thefurnace. Thereby, carbon black of small particle size and narrowagglomerate size distribution is obtained and damage to the reactor wallrefractory in the combustion section is minimized.

U.S. Pat. No. 7,655,209 relates to a so-called “deep fuel rich” processfor producing carbon black wherein the reactor off-gas is usedpreferably without natural gas or other supplementary combustible gasfeed streams with an oxidant gas stream providing oxygen in an amount ofless than 80% of stoichiometry in order to generate a combustion gas.Preferably, the off-gas is preheated, dewatered and, if necessary,carbon dioxide is removed. The content of hydrogen and carbon monoxidein the reactor off-gas is thereby utilized as combustible material. Theadvantage of the process is that the economics of the entire process isimproved due to a more complete use of the employed raw material,thereby considerably reducing the raw material costs. Despite theteaching in U.S. Pat. No. 7,665,209 to optionally remove carbon dioxidefrom the off-gas, utilizing hydrogen and carbon monoxide as predominantor sole combustible material will lead to an increased concentration ofcarbon dioxide in the generated combustion gas.

U.S. Pat. No. 3,438,732 discloses a process for the production of carbonblack wherein the tail gases from the production process are treated toremove hydrogen, carbon monoxide and water and are subsequently recycledto the process, preferably as atomizing gas for the carbon blackfeedstock. There, the inert gas resulting from the tail gassubstantially consists of nitrogen and carbon dioxide. Thereby, thecarbon black yield relative to the carbon black feedstock material canbe increased.

None of the above-discussed prior art documents addresses the problem ofcontrolling the porosity, particularly reducing the porosity of theresultant carbon black. The only product parameter that is disclosed asbeing influenced by the process regime in some of the above-discussedprior art references is the influence of combustion stoichiometry onparticle size and particle size distribution of the resultant carbonblack.

Thus, it is the object of the present invention to provide a process forthe production of carbon black that is suitable to control the porosityof the resultant carbon black, particularly to reduce the porosity ofthe carbon black.

It is a further object of the present invention to therebysimultaneously reduce the environmental impact of a carbon blackproduction process. It is particularly beneficial if the concentrationof gases detrimental to the environment like NO_(x), SO_(x) or CO₂ inthe reactor off gas could be reduced.

SUMMARY OF THE INVENTION

These objects have been attained by a furnace process for the productionof carbon black comprising:

-   -   feeding an O₂-containing gas stream, a fuel stream comprising        combustible material and optionally one or more further gas        streams to a furnace reactor;    -   subjecting the combustible material to combustion in a        combustion step to provide a hot flue gas stream, wherein the        O₂-containing gas stream, the fuel stream comprising combustible        material and optionally the one or more further gas stream are        fed to the combustion step in amounts providing a k factor of        less than 1.2, wherein the k factor is defined as the ratio of        O₂ theoretically necessary for stoichiometric combustion of all        combustible material in the combustion step to the total O₂ fed        to the combustion step;    -   contacting a carbon black feed stock with the hot flue gas        stream in a reaction step to form carbon black;    -   terminating the carbon black formation reaction in a terminating        step;        wherein the combined streams fed to the combustion step contain        less than 20.5 vol.-% O₂ and less than 3.5 vol. % of carbon        dioxide based on the total volume of gaseous components        excluding combustible components fed to the combustion step;        and/or        an inert gas stream comprising a combined amount of components        selected from oxygen containing compounds of at most 16 vol.-%        is fed to at least one of the reaction step and the terminating        step.

Employing the process according to the present invention furnace blackscan be produced having an STSA surface area of 130 m²/g to 350 m²/g,wherein

-   -   the ratio of BET surface area to STSA surface area is less than        1.1 if the STSA surface area is in the range of 130 m²/g to 150        m²/g,    -   the ratio of BET surface area to STSA surface area is less than        1.2 if the STSA surface area is greater than 150 m²/g to 180        m²/g,    -   the ratio of BET surface area to STSA surface area is less than        1.3 if the STSA surface area is greater than 180 m²/g; and        the STSA surface area and the BET surface area are measured        according to ASTM D 6556.

Preferably, the furnace black of the present invention has a STSAsurface area of 140 m²/g to 350 m²/g wherein

-   -   the ratio of BET surface area to STSA surface area is less than        1.1, preferably less than 1.09 if the STSA surface area is in        the range of 140 m²/g to 150 m²/g,    -   the ratio of BET surface area to STSA surface area is less than        1.2, preferably less than 1.15 if the STSA surface area is        greater than 150 m²/g to 180 m²/g,    -   the ratio of BET surface area to STSA surface area is less than        1.3, preferably less than 1.25 if the STSA surface area is        greater than 180 m²/g.

Furthermore, the present invention relates to an apparatus for running apreferred embodiment of the process according to the present inventioncomprising

-   -   a) a furnace reactor comprising        -   a first reaction zone for generating a hot flue gas stream            and at least one line in flow connection with the first            reaction zone for feeding an O₂-containing gas stream to the            first reaction zone and at least one line in flow connection            with the first reaction zone for feeding a fuel stream            comprising combustible material to the first reaction zone;        -   a second reaction zone for contacting the hot flue gas            stream with the carbon black feed stock downstream of and in            flow connection with the first reaction zone and at least            one line in flow connection with the second reaction zone            for feeding carbon black feed stock to the second reaction            zone; and        -   a third reaction zone for terminating the carbon black            formation reaction downstream of and in flow connection with            the second reaction zone comprising means for quenching the            carbon black formation reaction; and    -   b) an inert gas supply unit; and    -   c) at least one line connecting the inert gas supply unit to the        reactor or to any of the feeding lines for feeding material to        the reactor in order to feed an inert gas stream to the reactor,        wherein the inert gas supply unit (9) is selected from a supply        line connecting an external inert gas production facility to the        apparatus, a storage unit (9) or an air separation unit (9).

DETAILED DESCRIPTION OF THE INVENTION

The present inventors realized that the porosity of a furnace black canbe controlled by modifying the well-known furnace process.

In the process of the present invention an O₂-containing gas stream anda fuel stream comprising combustible material is fed to the combustionstep in a furnace reactor. The fuel stream is subjected in thecombustion step to combustion in order to provide a hot flue gas stream.The combustion step is conducted in a first reaction zone of the furnacereactor that may be referred to as the precombustion chamber. The hotflue gas stream thereby obtained has preferably a temperature in therange of 1,000 to 2,600° C., preferably 1,200 to 2,500° C., morepreferred 1,300 to 2,400° C. and most preferred 1,500 to 2,100° C. Thegeometry of the precombustion chamber is not critical for the process ofthe present invention and depends on the type of reactor used for theprocess. The geometry can be varied as known by a person skilled in theart in order to adjust the process to other requirements that are notessential to the present invention. Examples of suitable combustors aregiven in EP2361954 A1, U.S. Pat. No. 6,391,274 B1, DE 19521565 A1, U.S.Pat. No. 8,735,488 B2.

Due to the high temperatures of the flue gas generated, theprecombustion chamber is lined with appropriate refractory material thatcan be easily selected by a person skilled in the art depending on thetemperatures that are obtained during the process of the presentinvention. Alternatively the reactor walls can be cooled by a gas orliquid stream.

As fuel stream according to the present invention any material can beused that is combustible. Preferably, the fuel stream comprises liquidand/or gaseous hydrocarbons, the fuel stream contains at least 50 wt-%,more preferred at least 70 wt-%, even more preferred at least 90 wt-%,and most preferred at least 95 wt.-% of hydrocarbons. Particularlypreferred is the use of natural gas. Optionally, the fuel stream can bepre-heated prior to entry into the combustion zone.

As O₂-containing gas stream any gas stream can be used that comprisesoxygen gas. Particularly suitable is air, oxygen-reduced oroxygen-enriched air.

According to the present invention, the O₂-containing gas stream, thefuel stream and optionally the inert gas stream are fed to thecombustion step in the furnace reactor in amounts providing a k factorof less than 1.2, wherein the k factor is defined as the ratio of O₂theoretically necessary for stoichiometric combustion of all combustiblematerial in the fuel stream to the total O₂ in the combustion step.Preferably, the k factor is 0.15 to 1.2, more preferred 0.3 to 1.15,even more preferred 0.75 to 1.15, particularly preferred 0.85 to 1.1,and most preferred 0.95 to 1.05. The person skilled in the art willappreciate that the k factor can be easily calculated from the contentand type of combustible material in the feed streams and the O₂ contentof the streams to the reactor and their respective flow rates.

The upper limit of the O₂ content of the combined streams fed to thecombustion step can be 20, 19.5, 19, 18.5, 18, 17.5, 17, 16.5, 16, 15.5,15, 14.5, 14, 13.5 or 13 vol.-% based on the total volume of gaseouscomponents excluding combustible components fed to the combustion step.The lower limit of the O₂ content of the combined streams fed to thecombustion step can be 1.0, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6vol.-% based on the total volume of gaseous components excludingcombustible components fed to the combustion step. The upper limit ofthe CO₂ content of the combined streams fed to the combustion step canbe less than 3, less than 2.5, less than 2.0, less than 1.5, less than1.0, less than 0.5 vol. % based on the total volume of gaseouscomponents excluding combustible components fed to the combustion step.

In the process according to the present invention the hot flue gasgenerated in the combustion step, i.e. the precombustion chamber, iscontacted in a reaction step with the carbon black feedstock. In thereaction step pyrolysis of the carbon black feedstock takes place andcarbon black is formed. According to the present invention, thecross-section of the furnace reactor in flow direction behind the firstreaction zone or precombustion chamber can be reduced or expanded. Thesection of the reactor in flow direction behind the first reaction zoneor precombustion chamber may form the second reaction zone wherepredominantly the carbon black-forming reaction occurs. The secondreaction zone in general expands from the point where the first carbonblack feed stock material enters the reactor to the point where thetermination of the carbon black formation reaction as described in moredetail below begins. The actual length and geometry of the secondreaction zone can be varied in wide ranges depending on the type ofreactor employed and the specific requirements of the process for theactually produced carbon black.

In general, the carbon black feedstock material can fed to the reactionstep by any suitable means. The carbon black feedstock material can beinjected radially, for example by using radial lances or axially byusing one or more axial lances into the second reaction zone. Anysuitable carbon-containing material known to the person skilled in theart as suitable for carbon black production can be employed. Suitablecarbon black feedstock can be selected from liquid and gaseoushydrocarbons such as coal tar oils, steam cracker oils, catcracker oils,natural oils or natural gas. It is particularly useful to employ theabove-mentioned liquid hydrocarbon-containing oils as carbon blackfeedstock material.

In the terminating step the carbon black formation reaction isterminated, Termination can be conducted downstream of the secondreaction zone in a third reaction zone which is also referred to asquenching zone. Termination of the carbon black formation reaction canbe achieved by any means known to the person skilled in the art.Thereby, the formed carbon black as well as the reactor off-gas arecooled and the carbon black formation reaction is terminated. Coolingcan be achieved by direct or indirect heat exchange, for example byusing cooled reactor walls, a quench boiler, or quenching. Preferably,quenching is achieved be injecting a suitable quench liquid. Accordingto the present invention, it is also suitable that the cross-section ofthe furnace reactor in the quenching zone is increased compared to thesecond reaction zone. The quench liquid can be injected at variouspositions in the furnace reactor, depending on the desired properties ofthe carbon black to be produced. The quench liquid can be injectedaxially and/or radially at different positions of the reactor. Of courseit is also possible to use any combination of the different possibleinjection points for the quench liquid. Preferably, water is used as aquench liquid.

A particular advantage of the present invention is that in order toproduce low porosity carbon blacks the process is not restricted anylonger to use quench positions in proximity of the second reaction zone.Thus, a wider range of carbon blacks having the desired properties, butstill having a low porosity, can be produced since the porosity is notany longer determined only by the quench position, as is well known to aperson skilled in the art, as discussed above in the introductory part.

The reaction mixture comprising the formed carbon black as well as thereactor off-gases after leaving the quenching zone of the reactor ispreferably directed through a heat exchanger. Thereby, the reactionmixture is cooled to allow further processing such as separation of theformed carbon black from the reactor off-gas. Furthermore, in the heatexchanger the O₂-containing gas used for combusting the fuel stream canbe preheated in order to increase the overall energy efficiency of theprocess. A single or multiple heat exchangers can be used in order toreduce the temperature of the reaction mixture to an appropriate levelfor further processing.

Subsequently, the reaction mixture is subjected to a gas/solidseparation operation in order to separate the carbon black from thereactor off-gases. Typically, filters are used for separation of thecarbon black from the reactor off-gases. Further treatment steps for theobtained carbon black and the reactor off-gas may follow.

The object of the present invention, as discussed above, is attained bycompared to a standard furnace process adjusting the k factor to be lessthan 1.2 and increasing the inert gas concentration in the reactor whilelimiting the amount of CO₂ fed to the reactor.

This is achieved according to the present invention by feeding combinedstreams to the combustion step providing less than 20.5 vol.-% O₂ andless than 3.5 vol. % of carbon dioxide based on the total volume ofgaseous components excluding combustible components fed to thecombustion step. Alternatively an inert gas stream comprising a combinedamount of components selected from oxygen containing compounds of atmost 16 vol.-% is fed to at least one of the carbon black formation stepand the terminating step. As understood by a person skilled in the artboth measures can also be combined.

As inert gas any gas can be used that does not interfere with the carbonblack production process at the reaction conditions prevailing withinthe reactor. Thus, the inert gas stream should comprise a combinedamount of components selected from oxygen-containing compounds of atmost 16 vol.-%. Suitable upper limits for the amount ofoxygen-containing compounds, are at most 15% vol.-%, at most 14% vol.-%,at most 13% vol.-%, at most 12% vol.-%, at most 11% vol.-%, at most 10%vol.-%, at most 9% vol.-%, at most 8% vol.-%, at most 7% vol.-%, at most6 vol.-%, at most 5 vol.-%, at most 4 vol.-% or at most 3 vol.-%. Lowerlimits of the amount of oxygen-containing compounds can be 0.01 vol.-%,0.1 vol.-%, 0.3 vol.-%, 0.5 vol.-%, 1 vol.-% or 2 vol.-%. Particularly,the combined amount of molecular oxygen, any kind of oxidative compoundssuch as nitrogen oxides as well as water, carbon monoxide and carbondioxide should be controlled to be below the specified levels. Suitableinert gases can be selected from N₂-containing gases comprising at least84 vol.-% N₂; and ammonia. N₂-containing gases are particularlypreferred to be used as inert gas. Suitable N₂-containing gases comprise84-99.9999 vol.-% N₂, more preferred 90-99.99 vol.-% N₂, even morepreferred 92-99.99 vol.-% N₂, most preferred 95-99 vol.-% N₂.

Since the reactor off-gas contains considerable amounts of water, CO andCO₂ the reactor off-gas can only be used as inert gas after all of thesecomponents have been removed below the above-described levels. This isin most cases economically unattractive. Therefore, it is preferred ifthe inert gas is not derived from the reactor off-gas.

According to the present invention, inert gas can be fed directly orindirectly to the combustion step, the reaction step, the terminationstep or any combinations thereof. For example, it is possible that theinert gas is combined with the O₂-containing gas stream either prior topreheating the O₂-containing gas stream in the heat exchanger or withthe already preheated oxygen-containing gas stream. Alternatively theinert gas stream can be directly fed to the combustion step. It is alsopossible to introduce the inert gas to the reaction step for example byusing it as atomizing gas for the carbon black feedstock. Of course alsoany combinations thereof can be employed. It is particularly preferredto combine the inert gas stream with the O₂-containing gas stream priorto preheating.

In case the inert gas stream contains O₂ and is fed directly orindirectly to the combustion step a person skilled in the art willappreciate that the O₂ introduced to the combustion step by the inertgas stream has to be considered when calculating the k-factor accordingto the present invention. Thus, an inert gas stream containing O₂ thatis directly or indirectly fed to the first reaction zone can be at leastpart of the O₂-containing gas stream for generating the hot flue gasesaccording to the present invention.

Instead of or in combination to feeding an inert gas stream to thereactor including all above described embodiments an O₂-containing gasstream having compared to air a reduced content of oxygen containingcompounds can be fed to the combustion step. In this embodiment theO₂-containing gas stream fed to the combustion step comprises a combinedamount of components selected from oxygen containing compounds of lessthan 20.5 vol.-%. Particularly the combined amount of molecular oxygen,any kind of oxidative compounds such as nitrogen oxides as well aswater, carbon monoxide and carbon dioxide should be controlled to bebelow the specified levels. Of course the O₂ containing gas stream needsto contain sufficient oxygen to sustain combustion of the fuel streamand to obtain the k factor according to the present invention.Furthermore if the oxygen gas content is too low the process can beun-economical since then to high flow rates of the O₂-containing gasstream are required to adjust the k factor within the limits of thepresent invention. Thus the content of O₂ in the O₂-containing gas forthis embodiment is preferably 1 to 20.5 vol.-%. Suitable upper limitsfor the content of O₂ in the O₂-containing gas are 20, 19.5, 19, 18.5,18, 17.5, 17, 16.5, 16, 15.5, 15, 14.5, 14, 13.5 or 13 vol.-%. The lowerlimit of the O₂ content in the O₂-containing gas can be 1.0, 1.5, 2,2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6 vol.-%.

A k-factor approaching stoichiometric combustion of the fuel streamleads to temperatures of the resulting hot flue gas that areconsiderably higher compared to an oxygen-rich combustion scheme with alow k-factor. Feeding of the inert gas directly or indirectly into thefirst reaction zone and/or using an O₂-containing gas stream having areduced content of oxygen containing compounds, i.e. to thepre-combustion chamber, has the additional advantage that thetemperature of the hot flue gases is thereby reduced to some extent inorder to limit thermal stress for the lining of refractory material inthe reactor.

The inert gas is preferably nitrogen. The nitrogen can be provided tothe process of the present invention from any available sources. It isalso possible to use nitrogen gas of low purity as long as the combinedamount of components selected from oxygen containing compounds is lessthan 16 vol.-%. Thus, it is also possible to use nitrogen enrichedprocess gases from the carbon black process or other industrialprocesses as long as they are purified to the extent to fulfill theabove-defined limits of oxygen containing compounds. But as mentionedabove it is preferred not to use an inert gas that is derived from thereactor off-gas of the carbon black production process. Inert gas flaskbundles or inert gas storage tanks can be connected via lines to theappropriate locations of the furnace reactor employed in the process ofthe present invention at the suitable feeding points, as discussedabove. Alternatively, the inert gas preferably nitrogen can be fed viapipelines from external inert gas production facilities to the processaccording to the present invention.

Preferably, nitrogen is produced by separating nitrogen from air usingany kind of air separation process known to the person skilled in theart. Suitable readily available and economic processes for producingnitrogen of the required purity include pressure swing adsorptionprocesses and membrane separation processes. The pressure swingadsorption process is particularly preferred. Thereby, pressurized airis fed to a pressure swing adsorption unit wherein the oxygen isadsorbed at high pressure in the range of 8 to 12, preferably about 10bar on a carbon molecular sieve. Thereby, nitrogen of suitable purity(92 to 99.99 vol.-% N₂, preferably 95 to 99 vol.-% N₂) is obtained. Thisnitrogen then can be used as inert gas in the process of the presentinvention. The adsorbed oxygen is desorbed from the carbon molecularsieve at ambient pressure (approximately 1 bar) or reduced pressure. Thethus obtained oxygen can be either used in possible subsequent steps inthe carbon black production. Alternatively the oxygen can be used in aprocess other than a carbon black producing process.

Thus, the present invention also relates to an apparatus wherein aninert gas supply unit being a supply line connecting an external inertgas production facility to the apparatus, a storage unit or an airseparation unit, preferably a pressure swing adsorption unit or membraneseparation unit for separating air into a nitrogen-containing inert gasstream and an oxygen-enriched gas stream is connected to a furnacereactor or to any of the feeding lines for the O₂-containing gas, thefuel stream, the carbon black feedstock or the quench material to thereactor in order to feed inert gas to the reactor.

According to a preferred embodiment the apparatus comprises at least oneheat exchanger unit for pre-heating the O₂-containing stream with thehot reaction mixture leaving the furnace reactor. The inert gas supplyunit, preferably the pressure swing adsorption unit or membraneseparation unit is connected via a feeding line for the inert gas to thefeeding line of the O₂-containing stream prior to entry into the heatexchanger.

By using the process of the present invention furnace blacks can beproduced that despite their large external surface area (STSA surfacearea) have a low porosity. The STSA surface area is a measure of theexternal surface of the carbon black which correlates with particlesize. The smaller the carbon black particles, the larger is the externalsurface area. The BET surface area is a measure of external and internalsurface area. As a consequence, the ratio of BET surface area to STSAsurface area is an indication for the porosity of the carbon blacks. Ifthe ratio of BET to STSA surface area is approximately 1, the carbonblack has no porosity. In general, particularly with carbon blackshaving a small particle size and thus a large external surface area orSTSA area, also the ratio of BET surface area to STSA surface areasignificantly deviates from unity indicating that these carbon blackshave a high porosity. Thus, it is a surprising result that the processof the present invention leads to carbon blacks having a large externalsurface area, but still low porosity.

The furnace blacks according to the present invention have an STSAsurface area of 130 m²/g to 450 m²/g, preferably 140 m²/g to 300 m²/g,more preferred 150 m²/g to 280 m²/g, most preferred 160 m²/g to 250m²/g.

For the furnace blacks according to the present invention the ratio ofBET surface area to STSA surface area is less than 1.1 if the STSAsurface area is in the range of 130 m²/g to 150 m²/g or 140 m²/g to 150m²/g, the ratio of BET surface area to STSA surface area is less than1.2 if the STSA surface area is in the range of 150 m²/g to 180 m²/g,and the ratio of BET surface area to STSA surface area is less than 1.3if the STSA surface area is greater than 180 m²/g. Preferably, the ratioof BET surface area to STSA surface area is less than 1.09 if the STSAsurface area is in the range of 130 m²/g to 150 m²/g, the ratio of BETsurface area to STSA surface area is less than 1.15 if the STSA surfacearea is in the range of 150 m²/g to 180 m²/g, and the ratio of BETsurface area to STSA surface area is less than 1.25 if the STSA surfacearea is greater than 180 m²/g.

Furthermore, the furnace blacks according to the present invention canhave an OAN value of 100-150 ml/100 g

A particularly preferred furnace black according to the presentinvention exhibits an STSA surface area of at least 130 m²/g wherein

-   -   the ratio of BET surface area to STSA surface area is less than        1.09 if the STSA surface area is in the range of 130 m²/g to 150        m²/g or 140 m²/g to 150 m²/g,    -   the ratio of BET surface area to STSA surface area is less than        1.15 if the STSA surface area is greater than 150 m²/g to 180        m²/g,    -   the ratio of BET surface area to STSA surface area is less than        1.25 if the STSA surface area is greater than 180 m²/g;        and an OAN value in the range of 100-150 ml/100 g.

Furthermore, the furnace blacks of the present invention can have aniodine number greater than 125.

The carbon black properties as indicated throughout the presentapplication are measured as follows:

BET surface area and STSA surface area according to ASTM D-6556 (2014)

OAN according to ASTM D-2414 (2013)

Iodine number according to ASTM D-1510 (2013)

It is a further surprising result, that the process according to thepresent invention allows not only for the control of, particularly thereduction of the porosity of the carbon blacks produced by the processbut also to a reduction of the concentration of compounds in the off gasof the reactor, that are considered to be harmful to the environment.Particularly the concentration of NO_(x) and/or SO_(x) in the off-gascan be reduced, as will be shown in the experimental data.

A further advantage of the process according to the present invention isthat the amount of carbon black formed relative to employed feed stockcan be considerably increased compared to furnace processes where theconcentration of inert gas in the reactor is not increased. Thus, theprocess of the present invention is not only suitable to control, i.e.reduce, the porosity of furnace blacks, but in combination oralternatively leads to an improvement of the overall economics of theprocess indicated by increased carbon black yield. Thereby, also theoverall carbon dioxide balance of the process according to the presentinvention is improved. Thus, the present invention also provides aprocess for increasing the carbon black yield and for reducing CO₂emissions from the process. As a consequence, a more economic andenvironmentally acceptable process for producing carbon black isprovided.

The present invention will now be explained in more detail withreference to the figures and to the examples.

FIG. 1 shows a schematic representation of the process and the apparatusaccording to the present invention.

As depicted in FIG. 1, the process according to the present invention isconducted in a furnace reactor 1 having in flow direction three distinctreaction zones. To the first reaction zone 2, also referred to as thecombustion zone, a fuel stream comprising combustible material is fedvia line 5 and an O₂ containing gas stream via line 6. The fuel streamis subjected in the first reaction zone 2 to combustion in order toprovide hot flue gases. As shown in FIG. 1, the diameter of the furnacereactor is narrowed, forming a second reaction zone 3 where carbon blackfeedstock is contacted with the hot flue gases. The carbon blackfeedstock is fed via line 7 to the second reaction zone 3 in the narrowpart of the furnace reactor. This can be achieved by a plurality ofradially arranged injection ports like oil lances (not shown).Alternatively or in addition, carbon black feedstock material can alsobe injected into the second reaction zone 3 via axial lances. In thesecond reaction zone 3 carbon black is formed by decomposition of thecarbon black feedstock material. The thereby produced pyrolysis reactionmixture enters the third reaction zone 4 that is also referred to as thequenching zone. The quench material can be fed to a plurality ofpositions via the quench material line 8 to the quench zone. In thequenching zone 4 the reaction mixture is cooled down to a temperaturethat is low enough to essentially terminate the carbon black formationreaction. At this point, the reaction mixture is a dispersion of carbonblack particles in a continuous gas phase of the reaction gases. Thereaction mixture, after leaving the furnace reactor, is directed to one(FIG. 1) or more heat exchange units 11, in order to further reduce thetemperature of the reaction mixture. The heat that is thereby removedfrom the reaction mixture is used to preheat the O₂-containing gasstream prior to entry into the first reaction zone 2. The coldO₂-containing gas stream is fed via line 13 to the heat exchange unit 11and the preheated oxygen-containing gas stream is fed via lines 6 to thefirst reaction zone 2.

FIG. 1 shows possible positions for feeding the inert gas stream to thereactor. One suitable position is to feed the inert gas from an inertgas storage or production unit 9 via line 10 to line 13 of the coldO₂-containing gas prior to entry into the heat exchanger 11. Asdiscussed above, unit 9 is preferably a pressure swing adsorption unit.Alternatively, the inert gas is fed via line 10 to line 6 feeding thepreheated O₂-containing gas stream to the first reaction zone 2. It isalso possible to feed the inert gas stream via line 10 directly to thereactor 1 into the first reaction zone 2. Most preferably, the inert gasstream is fed via line 10 to line 13 of the cold O₂-containing gas priorto entry into the heat exchanger 11.

The cooled solid/gaseous reaction mixture leaving the heat exchangerunit 11 is directed to a separation unit 14 where the carbon blackparticles are recovered from the reaction mixture. The separation unit14 is preferably a filter unit. The solid carbon black is furtherconducted to a discharge unit 15 for further processing and storage. Theseparated gas phase is then also directed to further processing unitsfor cooling and gas treatment before it is released to the environment.

In the examples as presented an apparatus as shown in FIG. 1 is used,wherein the carbon black feedstock is injected via 4 radially orientedoil lances into the second reaction zone 3. As inert gas nitrogen isused that is directly fed to line 13 of the cold O₂-containing gas priorto entry into the heat exchanger 11, 12. The process parameters and theproperties of the obtained carbon blacks are shown in Table 1.

TABLE 1 Example Unit CE1 E1 E2 Process parameter k-Factor 0.75 0.75 1.0combustion air flow Nm³/h 2302 2299 2302 combustion air temperature ° C.651 650 650 nitrogen gas flow Nm³/h 0 246.6 246.4 fuel (natural gas)flow Nm³/h 178.0 177.8 237.5 carbon black feedstock kg/h 493 493 493temperature oil lance (A-D) ° C. 116.5 116.5 116.4 pre-quench stream l/h657 656 656 post-quench stream m³/h 0.304 0.29 0.287 temperature reactorexit ° C. 795 794 795 temperature pre-combustion ° C. 1786 1703 1828chamber measured by IR molar fraction of CO in the % 13.03 11.1 9.09water free tail gas ¹ sulfur flow in tail gas ² kg/h 1.8 1.8 1.6 Carbonblack properties Iodine mg/g 207.1 180.7 166.6 BET m²/g 186.7 159.8146.3 STSA m²/g 147.7 139.3 134.4 BET:STSA 1.26 1.15 1.09 OAN ml/100 g142.1 140.2 153 ¹ Tail gas is extracted from the production line andfiltered to remove carbon black. Subsequently the tail gas is cooled to+4° C. to freeze out water and thereafter is passed through phosphorouspentoxide to remove water completely. The water free tailgas compositionis analyzed with an Inficon 3000 Micro GC Gas Analyzer to obtain themolar fraction of CO. The Inficon 3000 Micro GC Gas Analyzer isfrequently calibrated with specified reference gas. ² Sulfur flow intail gas is calculated via a mass balance. The sulfur flow of carbonblack is subtracted from the sulfur flow of the feedstock. Thedifference is the sulfur flow of tail gas. The sulfur content offeedstock and carbon black is analyzed with an,, vario EL cube“ CHNS -elemental analyzer from,, Elementar Analysesysteme GmbH. The sulfur flowof feedstock and carbon black is calculated taking into account the massflows of feedstock and carbon black and the sulfur concentration infeedstock and carbon black.

The invention claimed is:
 1. A process for the production of carbonblack with a furnace reactor, wherein the furnace reactor comprises, asthree distinct zones, and in order in a flow direction: a combustionzone, a reaction zone that extends from a point where carbon blackfeedstock material is first injected to a point where cooling of formedcarbon black begins, and a quench zone in which carbon black formationis terminated, wherein a cross-section of the quench zone is larger thana cross-section of the reaction zone, the process comprises: feedingcombined gas streams comprising an O₂-containing gas stream and a fuelstream comprising combustible material to the combustion zone of thefurnace reactor, wherein the combined gas streams are fed to thecombustion zone in amounts that provide a k factor of less than 1.2, thek factor being defined as the ratio of O₂ theoretically necessary forstoichiometric combustion of all combustible material in the combustionzone to the total O₂ fed to the combustion zone; combusting thecombustible material in the fuel stream in a combustion step in thecombustion zone to provide a hot flue gas stream, and passing the hotflue gas stream to the reaction zone; introducing a carbon blackfeedstock into the reaction zone, and contacting the carbon blackfeedstock with the hot flue gas stream passed from the combustion zonein a reaction step in the reaction zone to form carbon black; andterminating carbon black formation reaction by quenching in aterminating step in the quench zone; wherein an inert gas stream is fedto at least one of the combustion zone in the combustion step, thereaction zone in the reaction step, and the quench zone in theterminating step, the inert gas comprising a combined amount ofcomponents selected from oxygen containing compounds of at most 16vol.-% based on the total volume of gaseous components excludingcombustible components fed to the combustion step.
 2. The process ofclaim 1, wherein the inert gas stream is fed to: a supply line for theO₂-containing gas stream; a supply line for the fuel stream; a supplyline for the carbon black feedstock; a supply line for a quench materialused in the terminating step; or a combination thereof.
 3. The processof claim 2, wherein the furnace reactor further comprises a pre-heaterfor the O₂-containing gas stream; and the process further comprisesfeeding the inert gas stream to a supply line for the O₂-containing gasstream at a location upstream of the heat exchanger.
 4. The process ofclaim 1, wherein the inert gas is selected from N₂-containing gasescomprising at least 84 vol.-% N₂ based on the total volume of gaseouscomponents excluding combustible components fed to the combustion step,and ammonia.
 5. The process of claim 4, wherein the inert gas isselected from N₂-containing gases comprising 84-99.9999 vol.-% N₂ basedon the total volume of gaseous components excluding combustiblecomponents fed to the combustion step.
 6. The process of claim 5,wherein the inert gas is selected from N₂-containing gases comprising90-99.99 vol.-% N₂ based on the total volume of gaseous componentsexcluding combustible components fed to the combustion step.
 7. Theprocess of claim 6, wherein the inert gas is selected from N₂-containinggases comprising 92-99.99 vol.-% N₂ based on the total volume of gaseouscomponents excluding combustible components fed to the combustion step.8. The process of claim 7, wherein the inert gas is selected fromN₂-containing gases comprising 95-99 vol.-% N₂ based on the total volumeof gaseous components excluding combustible components fed to thecombustion step.
 9. The process of claim 1, further comprisingseparating air in an air separation unit into a nitrogen-containing gasstream and an oxygen-enriched gas stream, wherein thenitrogen-containing gas stream is employed as the inert gas stream. 10.The process of claim 9, wherein the air separation unit is a pressureswing adsorption unit or a membrane separation unit.
 11. A process forthe production of carbon black with a furnace reactor, wherein thefurnace reactor comprises, as three distinct zones, and in order in aflow direction: a combustion zone, a reaction zone that extends from apoint where carbon black feedstock material is first injected to a pointwhere cooling of formed carbon black begins, and a quench zone in whichcarbon black formation is terminated, wherein a cross-section of thequench zone is larger than a cross-section of the reaction zone, theprocess comprises: feeding combined gas streams comprising anO₂-containing gas stream and a fuel stream comprising combustiblematerial to the combustion zone of the furnace reactor, wherein thecombined gas streams are fed to the combustion zone in amounts thatprovide a k factor of less than 1.2, the k factor being defined as theratio of O₂ theoretically necessary for stoichiometric combustion of allcombustible material in the combustion zone to the total O₂ fed to thecombustion zone; combusting the combustible material in the fuel streamin a combustion step in the combustion zone to provide a hot flue gasstream, and passing the hot flue gas stream to the reaction zone;introducing a carbon black feedstock into the reaction zone, andcontacting the carbon black feedstock with the hot flue gas streampassed from the combustion zone in a reaction step in the reaction zoneto form carbon black; and terminating carbon black formation reaction byquenching in a terminating step in the quench zone; wherein the combinedgas streams fed to the combustion step contain less than 20.5 vol.-% O₂and less than 3.5 vol.-% of carbon dioxide based on the total volume ofgaseous components excluding combustible components fed to thecombustion step.
 12. The process of claim 11, wherein an inert gasstream is fed to at least one of the combustion zone in the combustionstep, the reaction zone in the reaction step, and the quench zone in theterminating step, the inert gas comprising a combined amount ofcomponents selected from oxygen containing compounds of at most 16vol.-% based on the total volume of gaseous components excludingcombustible components fed to the combustion step.
 13. The process ofclaim 11, wherein the k factor is in a range from 0.15 to 1.2.
 14. Theprocess of claim 13, wherein the k factor is in a range from 0.3 to1.15.
 15. The process of claim 14 wherein the k factor is in a rangefrom 0.15 to 1.2.
 16. The process of claim 15 wherein the k factor is ina range from 0.3 to 1.15.
 17. The process of claim 16 wherein the kfactor is in a range from 0.75 to 1.15.
 18. The process of claim 17wherein the k factor is in a range from 0.85 to 1.1.
 19. The process ofclaim 18 wherein the k factor is in a range from 0.95 to 1.05.
 20. Theprocess of claim 11, wherein the combined streams fed to the combustionstep comprise 1.0 to 20.0 vol.-% O₂ and/or less than 2.0 vol.-% ofcarbon dioxide based on the total volume of gaseous components excludingcombustible components fed to the combustion step.
 21. The process ofclaim 20, wherein the combined streams fed to the combustion stepcomprise 2.5 to 19.5 vol.-% O₂ and/or less than 1.0 vol.-% of carbondioxide based on the total volume of gaseous components excludingcombustible components fed to the combustion step.
 22. The process ofclaim 21, wherein the combined streams fed to the combustion stepcomprise 5.0 to 19.0 vol.-% O₂ and/or less than 0.5 vol.-% of carbondioxide based on the total volume of gaseous components excludingcombustible components fed to the combustion step.
 23. The process ofclaim 11, wherein the O₂-containing gas stream is air.
 24. The processof claim 11, wherein the fuel stream comprises natural gas.